Present day aerial radio communication systems, such as navigation and communication systems, distance measuring equipment, navigation aid systems, etc. customarily provide a cockpit console visual display of the frequency of the (navigation) channel to which an avionics receiver is tuned. In addition, they supply an audio output (in the form of a (Morse) encoded station identifier code) representative of the source (the transmitting station) of the monitored frequency, which has been superimposed or modulated onto the navigation signal. By listening to, mentally decoding, and/or referring to a published decoding reference, the series of dots and dashes of which the encoded signal is comprised, the pilot may determine the alpha-numeric abbreviation of the identification of the transmitting station. Given the fact that the degree of concentration required by the pilot in flying the aircraft is already considerable, it goes without saying that a mechanism that is capable of alleviating the pilot of this potentially distracting, code-deciphering burden would add an additional safety factor to the control of the aircraft. Now although there do exist Morse code-type trainer/monitor units, that are designed as desktop, stand-alone devices, and not as avionics-integrated subsystems, such devices are both physically incompatible with the cockpit environment and lack requisite noise immunity.
More particularly, presently commercially available code reader and display units, such those configured and functioning in the manner of the AR-501 Radio Telegraph Terminal, manufactured by AOR, Ltd. Japan or the Code*Star code reader, manufactured by Microcraft Corp., Mequon, Wisconsin, are designed to b used with commercial radio receivers for "off the air reception" or for personal telegraph Morse code training, and require that the code-modulated input frequency be an effectively `clean` noise (particularly voice)-free signal. Voice signals that are often present on an avionics communications channel, which such `trainer`-type decoder units are not designed to monitor, effectively prevent these types of units from generating a useful output, as the decoding circuitry attempts to respond to and decode the characteristics of the voice signal, and essentially locks up, generating no output.